Models for the downlink capacity of WCDMA systems with dedicated channels as specified in the UMTS Release '99 rely on the orthogonality factor for approximating the intra-cell interference due to multi-path propa...
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Models for the downlink capacity of WCDMA systems with dedicated channels as specified in the UMTS Release '99 rely on the orthogonality factor for approximating the intra-cell interference due to multi-path propagation. This model is no longer applicable for the HSDPA as the performance of fast scheduling and adaptive modulation and coding depends on the small-scale fading effects. This leads to the problem on how to produce reliable statistics for the long-term system-level behavior when small-scale fading effects are not negligible. In this paper we introduce a general framework on how to perform time-efficient simulations that capture the effects of small-scale fading.
In UMTS networks, the transmit power for the HSDPA can be a large fraction of the total transmit power of a NodeB. We investigate the impact of three HSDPA transmit power allocation schemes on the performance of a UMT...
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In UMTS networks, the transmit power for the HSDPA can be a large fraction of the total transmit power of a NodeB. We investigate the impact of three HSDPA transmit power allocation schemes on the performance of a UMTS system with dedicated channel users and HSDPA users. The continuous HSDPA power allocation scheme avoids large steps of the transmit power in order to prevent irregularities in the downlink power control of dedicated channels. In contrast, the traffic-aware scheme switches the HSDPA power on only if data has to be transmitted. The power-ramping scheme combines the continuous and the traffic-aware scheme. The simulation model considers the complete interference situation in the network and uses a novel model to calculate HSDPA bandwidths. The results quantify the performance loss with the continuous scheme caused by additional interference, and show that the power-ramping scheme leads to results close to the traffic-aware scheme.
The WiMAX technology based on the IEEE802.16 standard is currently the most prospective candidate for broadband wireless access networks. One of the key issues is the design of the MAC layer, in particular the multipl...
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The WiMAX technology based on the IEEE802.16 standard is currently the most prospective candidate for broadband wireless access networks. One of the key issues is the design of the MAC layer, in particular the multiple access scheme. The IEEE 802.16 standard specifies different scheduling services with individual mechanisms for accessing the channel on the uplink. The non-real-time polling service and the best-effort service mainly rely on a contention mechanism to submit bandwidth requests to the base station. These two services are currently used for all types of traffic with unknown characteristics, i.e. typically all traffic except for some special VoIP connection with known codec. In this paper, we evaluate and compare the performance of the contention mechanisms for fixed and mobile WiMAX.
The deployment of multimedia services in next- generation networks is a challenge due to the high configuration complexity of the streaming process in different stationary and mobile sub-networks and for various user ...
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The deployment of multimedia services in next- generation networks is a challenge due to the high configuration complexity of the streaming process in different stationary and mobile sub-networks and for various user devices. The session initiation protocol (SIP) has proven to be a suitable mechanism to handle the control of multimedia services in such networks. However, the current standardization and implementation of SIP do not allow the simultaneous coordination of multiple concurrent applications on a single device, as the prescribed realization of the SIP state machines (transactions) does not consider mutual access of applications to a single SIP stack. This paper presents a SIP- based mechanism for synchronized management of services in a shared environment. We have developed a middleware that facilitates the uniform access of multiple applications towards one or multiple SIP stacks to enable prioritization of services and centralized resource coordination of concurrent SIP applications on a single terminal or server.
The ubiquitous access to multimedia services anywhere and at any time requires flexible service accommodation to user requirements and to device capabilities. At mobility of persons and devices, it is possible to enfo...
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The ubiquitous access to multimedia services anywhere and at any time requires flexible service accommodation to user requirements and to device capabilities. At mobility of persons and devices, it is possible to enforce not only terminal-based adaptations, but also the media sessions can migrate from device to device to optimize the user experience. As the capabilities of mobile hand-held devices are limited, migrating sessions to close-by high-performance terminals like wall displays or in-home entertainment systems will indeed contribute to optimized device application and to more satisfactory media consumption. The current SIP/SDP framework can partially enable a session-migration process. However, SIP/SDP lacks advanced client-search and description capabilities. On the other hand, MPEG-21 DI can support sophisticated service descriptions but it misses a control-data exchange approach. Therefore, this paper proposes to merge concepts from IMS using SIP/SDP(ng) with MPEG-21 DI to implement a novel session migration concept based on standardized mechanisms.
Internet connectivity establishment (ICE) is becoming increasingly important for P2P systems on the open Internet, as it enables NAT-bound peers to provide accessible services. A problem for P2P systems that provide I...
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Internet connectivity establishment (ICE) is becoming increasingly important for P2P systems on the open Internet, as it enables NAT-bound peers to provide accessible services. A problem for P2P systems that provide ICE services is how peers discover good quality ICE servers for NAT traversal, that is, the TURN and STUN servers that provide relaying and hole-punching services, respectively. Skype provides a P2P-based solution to this problem, where super-peers provide ICE services. However, experimental analysis of Skype indicates that peers perform a random walk of super-peers to find one with an acceptable round-trip latency. In this paper, we discuss a self-organizing approach to discovering good quality ICE servers in a P2P system based the walk topology. The walk topology uses information about each peer's ability to provide ICE services (open IP address, available bandwidth and expected session times) to construct a topology where the "better" peers for providing ICE services cluster in the center of the topology; this adaptation of the super-peer search space reduces the problem of finding a good quality ICE server from a random walk to a gradient ascent search.
The requirements for Web applications concerning workflow execution, interaction, aesthetics, federation and Web service integration are steadily increasing. Considering their complexity, the development of these &quo...
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The requirements for Web applications concerning workflow execution, interaction, aesthetics, federation and Web service integration are steadily increasing. Considering their complexity, the development of these "rich workflow-based Web applications" requires a systematic approach taking key factors like strong user involvement and clear business objectives into account. To this end, we present an approach for the model-driven construction and evolution of such Web applications on the basis of workflow models which is founded on Domain-specific Languages (DSLs) and a supporting technical framework. We describe our approach's core DSL for workflow modeling which supports various modeling notations like BPMN or Petri nets and outline a set of DSLs used for designing workflow activities like dialog construction, data presentation and Web service communication. In conclusion, rich workflow-based Web applications can be built by modeling workflows and activities and passing them to the associated technical framework. The resulting running prototype can then be configured in detail using the presented DSLs.
Network Operators start to offer formerly hidden services such as location service, messaging services and presence services. This fosters the development of a new class of innovative context aware applications that a...
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As the complexity of parallel file systems' software stacks increases it gets harder to reveal the reasons for performance bottlenecks in these software layers. This paper introduces a method which eliminates the ...
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As the complexity of parallel file systems' software stacks increases it gets harder to reveal the reasons for performance bottlenecks in these software layers. This paper introduces a method which eliminates the influence of the physical storage on performance analysis in order to find these bottlenecks. Also, the influence of the hardware components on the performance is modeled to estimate the maximum achievable performance of a parallel file system. The paper focuses on the parallel virtual file system 2 (PVFS2) and shows results for the functionality file creation, small contiguous I/O requests and large contiguous I/O requests
In this paper the author describes the approaches to blending learning he has pursued at the University of Vienna's institute of distributed and Multimedia systems and at the University of South Australia's Sc...
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ISBN:
(纸本)9780769527758
In this paper the author describes the approaches to blending learning he has pursued at the University of Vienna's institute of distributed and Multimedia systems and at the University of South Australia's School of computer and Information science in an attempt to supply online students and on campus students with enhanced teaching and learning materials in an Information Security Management course
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